To block numbers on Android devices:
Open your Phone app
Click on the three dots in the right hand corner
Tap Blocked Numbers
Tap Add a number
Add the number you'd like to block
To prevent spam text messages:
Open the Google Messages app
Tap the three dots in the top-right corner.
Tap Spam protection
Turn on Enable spam protection
If you want to block a number that texted you recently:
Open the spam text
Tap the three dots icon in the top-right corner.
Tap block number
Reporting spam numbers
You can report spam numbers here.